Photographic paper prepared from partially acylated cellulose fibers



May 1964 w. H. GRIGGS ETAL 3,132,944

PHOTOGRAPHIC PAPER PREPARED FROM PARTIALLY ACYLATED CELLULOSE FIBERS Filed April 18, 1960 I AMMONIA TED COPOLYMER 0F w 5 TYRE/VE-MALE/C A/VHYDRIDE AND POLYGL YC/DYL E THEE PAPE/-? 0F PA CELLULOSE' A F/BEI? WILLIAM H. 617/665 ALA/V H. GRAY RALPH D ZAFFRANN INVENTORS United States Patent 3,132,944 PHOTOGRAPHIC PAPER PREPARED FROM PAR- TIALLY ACYLATED CELLULOSE FIBERS William H. Griggs, Alan H. Gray, and Ralph D. Zaffrann,

Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Apr. 18, 1960, Ser. No. 22,710 7 Claims. (Cl. 96-85) This invention relates to the manufacture of paper composed of partially esterified cellulose fibers improved in strength characteristics by sizing with styrene-maleic acid or styrene-maleic anhydride type resins having therewith a cross-linking agent.

Paper as ordinarily prepared is useful for numerous purposes such as for wrapping, writing paper, newsprint, printing paper and many other of the common uses for that material. However, papers have been found to be useful for special purposes and oftentimes modifications in the usual paper making processes to prepare paper for those special purposes are necessary. For instance, it is desirable that paper for photographic purposes exhibit good stability and be resistant to the imbibition of salts in processing operations. Paper subjected to aqueous baths has often been characterized by curling. This is particularly objectionable in photographic processing and in finished photographic products.

The application of a waterproof coating to paper for photographic purposes such as the application of a cellulose ester coating thereto has been suggested. Oftentimes, waterproofed paper exhibits a certain amount of stiifness and in many cases offers resistance to the application of a coating of an aqueous photographic emulsion thereon. The cost of preparing waterproofed paper for photographic purposes has often been high which has precluded its use in commercial manufacture.

It has been discovered in recent years that paper comprising cellulose fibers chemically combined with lower acid radicals exhibits properties superior to those of paper prepared from conventional wood pulp fibers. For instance, a paper prepared from cellulose fibers having a lower fatty acid radical content of -25%, apparent acetyl, exhibits good dimensional stability and freedom from appreciable curl. Also, paper of this type is characterized by low water and salt retention in comparision with many types of paper base which have been employed heretofore. It is desirable, however, in the case of paper prepared from partially acylated fibers that it exhibit high strength and good resistance to certain coating solvents.

One object of our invention is to provide a method for treating paper of partially acylated fibers whereby the strength of that paper is increased. Another object of our invention is to provide a method for treating paper from partially acylated fibers in which its resistance to the effects of certain coating solvents is enhanced. A further object of our invention is to prepare a partially acylated paper compatible with silver halide photographic emulsions. Other objects of our invention will appear herein.

We have found that an improvement in the characteristics of paper prepared from partially acylated cellulose fibers is obtained if that paper is sized with a styrenemaleic acid or anhydride resin together with a cross-linking catalyst (non-formaldehyde type) such as a small amount of diepoxide resin.

Partially acylated paper treated in accordance with our invention is composed of 75-100% of partially acylated cellulose fiber resulting from chemically combining cellulose fibers with fatty acid radicals of 2-4 carbon atoms so that the apparent acetyl content thereof of 3,132,944 Patented May 12, 1964 ice the acylated fiber is approximately 15-25%. The acylated fiber is dispersed in water to form an aqueous slurry and preferably beaten to a slowness useful for the paper making operations. Any other fiber used is present in an amount not more than 25% of the total fiber of the paper. This other fiber may be, for instance, wood pulp or rag fiber as is commonly used to make paper of sheet quality. After beating, the pulp slurry is applied to the wire of a paper machine preferably after incorporating a beater sizing therein such as by the method described in Griggs and Zaffrann application Serial No. 22,711, filed of even date. After the paper is formed and desirably after drying, it is then tub sized with a styrene-maleic anhydride or acid resin preferably after this resin has been mixed with a non-formaldehyde cross-linking agent such as diepoxide resin. The presence of diepoxide resin or other like cross-linkers contributes to the resistance to water, alcohol and aqueous alkali as may be used in imparting coatings to the paper.

The styrene resin materials which are useful in accordance with our invention for sizing partially esterified paper are water insoluble but alkali soluble and thus are first brought into solution in an alkaline material such as aqueous ammonia. This solution may then be applied as a sizing coating to the paper forming a coating which is insensitive to water but exhibits sensitivity to alkali or alcohol. The presence of diepoxide resin in the sizing coating causes the resin as a result of calendering and drying to impart resistance in the paper to the effect of alcohols such as might be employed in coating operations. For instance, in the curing of the styrene resin coated paper, a resistance against the dissolving effect of both alcohol and alkali is obtained.

The styrene resin which is employed as a sizing material applied to the surface of the paper is one obtained by the polymerization of styrene with maleic anhydride forming what may be termed a styrene-maleic anhydride polymer having the structure:

Instead of the styrene-maleic anhydride polymer, there may also be employed a partial ester of a polymer of this type such as one in which there is preferably approximately at least one acid group and up to one ester group per styrene unit, some of the carboxyl resulting from converting anhydride to acid having been reacted with alkyl such as methyl, ethyl, propyl or butyl. The structure of this partial ester polymer is represented by:

R being lower alkyl. It isusually preferable that the styrene-maleic anhydride copolymer and the partially esterified styrene-maleic polymer be employed in admixture with each other in any desired proportion such as equal parts of each. Although some variation is permissible in the amount of styrene resin on the base weight of the pulp, it is convenient to employ 0.25% of each (or 0.5% in all) of these resins, based on dry weight of fiber. This represents percentages resulting from the use of sizing solutions of 2% of each resin. The total styrene-maleic resin used may be from 0.25% up to 2% with good results being obtained.

After the styrene resin has been applied, the water may be driven off by a further drying and calendering operation to obtain the paper with the styrene-maleic resin sizing thereon. When ammonia is employed as the base in promoting the solution of these styrene-maleic resins,

the ammonium radical is ordinarily decomposed upon drying of the paper so that the paper is sized with the resin itself.

In the sizing of partially acylated paper with styrene resin sizing material in accordance with our invention, it is desirable to incorporate in that material a small amount of a nonaldehydic material which will promote cross-linking in the sizing operation. We have found that the presence of a small amount of a polyglycidyl ether is very effective in causing cross-linking of the styrenemaleic resin sizing material when the paper is subjected to either ordinary calendering or to a subsequent heat treatment. A polyglycidyl ether which has been found to be useful for this purpose is the reaction product of bis-phenolA and epichlorohydrin referred to as Polyether D in US. Patent No. 2,913,356 of Schroeder. This material is indicated to be substantially 2,2-bis(2,3-epoxypropoxyphenyl) propane. Other polyglycidyl ethers referred to in the Schroeder patent are useful for promoting the cross-linking of the styrene-maleic resins employed in accordance with our invention, particularly those referred to by letter such as Polyethers A, B, C, D and E. The polyglycidyl ether compounds useful as catalysts in sty rene resin sizing materials are commonly prepared by condensing a polyhydroxy compound such as a polyhydric alcohol or a polyhydric phenol with epichlorohydrin. For instance, a resinous polymeric epoxide resulting from the condensation of an epichlorohydrin and a polyhydric phenol is eminently useful in this connection.

After the paper has been tub sized with the styrenemaleic resin, with epoxy resin incorporated therein, it is subjected to a drying and calendering operation whereby the sizing material is cured forming a smooth surface, ordinarily at a temperature in the vicinity of ISO-180 F. Still further improvement may be obtained by heat treatment of the paper such as in oven or by infrared rays at a temperature on the order of 350 F. as described and claimed in our application Serial No. 22,675 of even date. We have found that by sizing partially acylated fiber paper in accordance with our invention, substantial increases are obtained in mullen and wet tensile strength and the sizing resistance is somewhat better than that of paper prepared from partially acylated cellulose fibers which have not been so sized.

A representative paper in accordance with our invention is shown in greatly enlarged cross-sectional view in the accompanying drawing wherein the layer is paper sheeting at least 75% of which is composed of partially acylated (PA) cellulose fibers. This paper contains a tub size coating 11 composed of ammoniated copolymer of styrene and maleic compound, e.g., maleic anhydride, and polyglycidyl ether catalyst. If desired a photographic emulsion layer may be applied upon the tube sized paper shown.

The following examples illustrate the preparation of paper of good quality both with and without utilization of our invention and a comparison of the characteristics obtained.

EXAMPLE 1 A roll of paper was prepared from cellulose fibers having a combined acetyl content of approximately which had been internally sized with 7% starch, 2% of a cationic thermosetting polyamide-epichlorohydrin resin as described in Example 1 of US. Patent No. 2,926,154 and of stearoyl hexadecylethenone (alkyl ketene dimer), all based on the weight of the fiber, dyes also having been added, as prepared from beaten partially acetylated fibers in a manner as described in Griggs and Zalfrann application Serial No. 786,041, filed January 12, 1959. Half of the roll of paper was tub sized with a 2% gelatin aqueous solution. The other half of the roll of paper was tub sized with a solution in aqueous ammonia of 2% of a styrene-maleic anhydride resin and 2% of a styrene-maleic acid resin, part of the carboxyl of which had been esterified with lower alkyl groups, which solution also contained as a catalyst a small portion of a polyglycidyl ether (Eponite-l00, a. water soluble glycidyl ether of a polyhydric alcohol) which was followed by a second tub size of gelatin solution containing no hardener. This left approximately 0.5% of styrene-maleic resin on the paper. The paper thus obtained was dried and supercalendered. The papers obtained were both tested with the results given in columns A and B of Table I, which follows. It is to be noted that there was a 25% increase in mullen and a 40% increase in wet tensile strength in the case of the paper in column B over that of column A and in addition, the sizing resistance was good in both cases.

EXAMPLE 2 A roll of paper was prepared from partially acetylated fibers in a manner similar to that described in the preceding example except that only A of the furnish was beaten and /3 thereof was subjected to a hydropulping operation. Titanium dioxide, dyes, optical brightener, starch, cationic thermosetting resin and stearoyl hexadecylethenone were added and paper sheet was prepared from the slurry of partially acetylated cellulose wood pulp. Half of the roll of paper thus prepared was tub sized with a 2% gel atin solution, dried, and water finished to obtain a desirable surface. The balance of the roll was tub sized first with aqueous ammonia containing 2% of styrene-maleic anhydride resin and 2% of partially esterified styrene maleic acid resin containing a catalytic amount of polyglycidyl ether and then with an aqueous solution of gelatin. The resulting paper was dried and waterfinished. The physical properties of the two papers were tested and the results of those tests are given in columns C and D of Table I presented below. It was found that the paper which had been sized with the styrene-maleic resin sizing as compared with that not so sized, showed a 33% increase in mullen and a 55% increase in wet tensile strength along with an increase in Valley penetration resistance plus a little decrease in Cobb size value. The second tub size with gelatin following the styrene resin size when the photographic emulsion coated thereover contains hardener serves to prevent emulsion frill during processing when the paper is employed for photographic purposes. The papers described in the above examples were coated with gelatin-silver halide photographic emulsions and the resulting products exhibited the usual advantages of partially acylated paper base and in the case of the papers in accordance with the invention, the photographic paper obtained exhibited added handling latitude due to the added strength supplied thereto. None of the photographic papers in the above examples exhibited emulsion frill or fiecking during either tray or machine processing in photographic processing solutions.

The following table gives the values obtained upon testing the various papers which had. been prepared:

Table l B D A Styrene- C Styrene- Control maleie Control maleie gel size rosin gel size resin sized sized Weight (lbs/1000 sq. in)..." 20 24 23 24 Thickness (0.001 in.) 4. 6 5. 4 4. 3 4. 7 Elmendori Tear L (in kg)--- 00 72 81 84 C 72 92 86 87 Perkins Mullen (in p.s.i.) 35 44 27 36 Wet tensile strength (hecto grams) 26 44 23 30 Penetration (Valley) 2000+ 2000+ 514 2000+ Expansion (2 min. in water) 1.55 1.55 1.55 1.80 Fold L (111.1.1.) 29!) 187 69 84 C 200 127 50 70 Percent Swell- 34 37 39 32 Percent Bulk. 14 18 15 8. 5 5 min. Cobb size (water) 0. 18 0. 13 0.16 0. 144

The swell and bulk values are obtained from the following formulas after determining the dry thickness by soaking the paper for minutes in water at room temperature and in the case of the former, determining the wet thickness and in the case of the latter, redrying the paper to about 5% moisture content and determining the redried thickness.

Wet thickness-dry thickness Dry thickness Wet redried thickness dry thickness Dry thickness Samples of partially acylated paper which had been internally sized with aluminum stearate and cationic thermosetting polyamide-epichlorohydrin resin, as described in Griggs and Zaifrann application Serial No. 22,711, filed of even date, were surface sized with styrenemaleic resin sizing in the manner described in Examples 1 and 2. These papers exhibited characteristics superior to those of like paper which had been surface sized with gelatin rather than having a sizing of styrene-maleic resin thereon. Both the mullen and wet tensile were superior to those of the paper to which no styrene-maleic resin sizing had been applied.

The paper prepared as described in accordance with our invention is eminently useful either with or without a baryta (BaSO +gelatin) coating as a support for gelatino-silver halide photographic emulsions. In those cases where the emulsion layers are unhardened, it is usually desirable to omit the gelatin coating of the paper, the emulsion then being applied directly to the styrenemaleic resin size layer, with or without first coating with baryta.

We claim:

1. A method of making paper which comprises app1ying to a paper sheet, the fibers of which have been beater sized and at least 75% of which are partially acylated cellulose fibers having an apparent acetyl content of 15-25%, 0.252%, based on the dry weight of the fibers, of a tub sizing essentially consisting of an aqueous solution of ammoniated copolymer of a styrene and maleic compound selected from the group consisting of maleic anhydride, maleic acid, maleic lower alkyl half esters and mixtures thereof containing a catalytic amount of polyglycidyl ether prepared by condensing a polyhydroxy compound selected from the group consisting of polyhydric alcohols and polyhydric phenols with epichlorohydrin followed by heat-drying and calendering the same whereby curing of the tub sizing occurs.

2. A method of making paper which comprises applying to a paper sheet, the fibers of which have been beater sized and at least 75% of which are partially acylated cellulose fibers having an apparent acetyl content of 15-25%, the beater sizing being cationic thermosetting polyamide-epichlorhydrin resin, 0.252%, based on the dry weight of the fibers, of a tub sizing essentially consisting of an aqueous solution of ammoniated copolymer of a styrene and maleic compound selected from the group consisting of maleic anhydride, maleic acid, maleic lower alkyl half esters and mixtures thereof containing a catalytic amount of polyglycidyl ether prepared by condensing a polyhydroxy compound selected from the group consisting of polyhydric alcohols and polyhydric phenols with epichlorohydrin followed by heat-drying and calendering the same whereby curing of the tub sizing occurs.

3. A method of making paper which comprises applying to a paper sheet, the fibers of which have been beater sized with cationic thermosetting polyamide-epichlorhydrin resin, at least 75 of which fibers have combined acetyl content of 1525%, 0.252%, based on the dry Percent swell= X 100 Percent bulk: X 100 weight of the fibers, of a tub sizing essentially consisting of an aqueous solution of a mixture of ammoniated copolymers of styrene-maleic anhydride and styrene-maleic lower half esters containing a catalytic amount of 2,2-bis- (2,3-epoxypropoxyphenyl)propane, followed by heatdrying and calendering the same whereby curing of the tub sizing occurs.

4. Paper composed of beater sized cellulose fibers, at least of which are partially acylated cellulose fibers having an apparent acetyl content of 1525% and tub sized with 0.252%, based on the dry weight of the fibers, of a mixture of ammoniated copolymer of a styrene and maleic compound selected from the group consisting of maleic anhydride, maleic acid and maleic lower alkyl half esters and a catalytic amount of polyglycidyl ether prepared by condensing a polyhydroxy compound selected from the group consisting of polyhydric alcohols and polyhydric phenols with epichlorohydrin.

5. Paper composed of cellulose fibers, at least 75 of which have an acetyl content of 15-25% chemically combined therewith, which paper is internally sized with aluminum stearate and cationic thermosetting polyamideepichlorhydrin resin and surface sized with a sizing essentially consisting of 0.252%, based on the dry weight of the fibers of ammoniated copolymer of styrene and maleic compound selected from the group consisting of maleic anhydride, maleic acid and maleic lower alkyl half esters and a catalytic amount of 2,2-bis(2,3-epoxypropoxyphenyl propane.

6. A photographic paper containing a gelatin-silver halide photographic emulsion layer applied to a paper support at least 75% of the fibers of which are partially acylated to an apparent acetyl content of 1525%, which fibers are beater sized, which paper is surface sized with a sizing essentially consisting of 0.252%, based on the dry weight of the fiber, of ammoniated copolymer of styrene and maleic compound selected from the group consisting of maleic anhydride, maleic acid and maleic lower alkyl half esters containing a catalytic amount of polyglycidyl ether prepared by condensing a polyhydroxy compound selected from the group consisting of polyhydric alcohols and polyhydric phenols with epichlorohydrin.

7. A photographic paper containing a gelatin-silver halide photographic emulsion applied to a paper support composed of cellulose fibers partially acylated to an acetyl content of 15-25%, which paper is internally sized with aluminum stearate and cationic thermosetting polyamideepichlorhydrin resin and surface sized with a sizing essentially consisting of 0.252%, based on the dry weight of the fiber, of a mixture of ammoniated styrene-maleic acid copolymer and styrene-maleic lower alkyl half ester copolymer containing therein a catalytic amount of 2,2-bis- (2,3-epoxypropoxyphenyl)propane.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,483 Castan July 20, 1943 2,348,001 Gibson et a1 May 2, 1944 2,607,761 Seymour Aug. 19, 1952 2,723,195 Blake Nov. 8, 1955 2,739,062 Griggs et a1 Mar. 20, 1956 2,765,228 Jordan Oct. 2, 1956 2,913,356 Schroeder Nov. 17, 1956 2,925,340 Bryce et al Feb. 16, 1960 2,926,116 Keim Feb. 23, 1960 2,926,154 Keim Feb. 23, 1960 2,992,156 Schulwitz July 11, 1961 3,002,860 Bishop Oct. 3, 1961 3,015,537 Gray Jan. 2, 1962 

6. A PHOTOGRAPHIC PAPER CONTAINING A GELATIN-SILVER HALIDE PHOTOGRAPHIC EMULSION LAYER APPLIED TO A PAPER SUPPORT AT LEAST 75% OF THE FIBERS OF WHICH ARE PARTIALLY ACYLATED TO AN APPARENT ACETYL CONTENT OF 15-25%, WHICH FIBERS ARE BEATER SIZED, WHICH PAPER IS SURFACE SIZED WITH A SIZING ESSENTIALLY CONSISTING OF 0.25-2%, BASED ON THE DRY WEIGHT OF THE FIBER, OF AMMONIATED COPOLYMER OF STYRENE AND MALEIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF MALEIC AMHYDRIDE, MALEIC ACID AND MALEIC LOWER ALKYL HALF ESTERS CONTAINING A CATALYTIC AMOUNT OF POLYGLYCIDYL ETHER PREPARED BY CONDENSING A POLYHYDROXY COMPOUND SELECTED FROM THE GROUP CONSISTING OF POLYHYDRIC ALCOHOLS AND POLYHYDRIC PHENOLS WITH EPICHLOROHYDRIN. 